The present invention relates to a case of the kind incorporating wheels for supporting the case on a floor so that the case can be wheeled about. Examples of disclosures known to the present applicants of cases having wheels are U.S. Pat. No. 4,036,336, U.S. Pat. No. 3,522,955, DE No. 1184472, DE No. 3339913 and U.S. Pat. No. 4,261,477. The latter two references disclose retractable handles but these handles are mounted independently of the wheels.
Wheels which rotate about axes which are fixed with respect to the outside of the main body of a case are likely to suffer damage and are likely to cause damage to other articles, particularly if the wheels are large. Small wheels are unsatisfactory for wheeling a case over a floor which has irregularities. In U.S. Pat. No. 4,122,924, U.S. Pat. No. 1,895,677, GB No. 1,581,310, GB No. 1,512,020, GB No. 2,124,589. DE No. 201271 and EP No. 187318, there are disclosed cases having retractable wheels and handles mounted independently of the wheels. The arrangements for extension and retraction of the wheels and handles are inconvenient. DE No. 806704 discloses retractable wheels and a handle which is detatchably mounted on the wheels. However, extension and retraction of the wheels is still inconvenient and must be performed individually for each wheel.
In U.S. Pat. No. 3,178,197, there is proposed a case having retractable wheels, a telescopic handle and a rack and pinion mechanism connecting the handle with respective carriers of the wheels, the arrangement being such that extension of the handle causes the wheels automatically to project from the body of the case. This avoids some of the inconvenience of the aforementioned proposals but the rack and pinion mechanism, if of sufficiently robust construction to operate reliably and freely over a prolonged service life, will necessarily contribute considerably to the weight of the case. Furthermore, a substantial proportion of the overall volume of the case is required to accommodate the wheels, wheel carrier and rack and pinion mechanism.
Disclosures of cases having retractable wheels mounted on respective pivoted carriers, movable handles and linkages connecting the handles with the wheel carriers are U.S. Pat. No. 3,141,680, U.S. Pat. No. 4,254,850, U.S. Pat. No. 2,510,754, GB No. 655,641, GB No. 1,444,998, GB No. 2,168,035, GB No. 2,135,638 and EP No. 142770. The case proposed in the latter specification has four wheels positioned near to respective corners of one major face of the case so that, when the case rests on its wheels, the opposite major face is at least approximately horizontal and provides a suitable platform to receive a stack of additional cases. Thus, the case disclosed in EP 142770 is suitable for carrying several additional cases. Furthermore, the case will be stable, when standing on a flat floor on all of its wheels, even when bearing a heavy load of additional cases. However, the wheels of the case disclosed in EP No. 142770 are small and are therefore unsuitable for supporting a heavy load of cases for movement on a floor which has any irregularities. Furthermore, a considerable proportion of the overall volume of the case must be devoted to accommodation of the retracted wheels and of the linkage connecting the wheel carriers to one another and to the handle. The wheels, linkage and handle contribute considerably to the weight and to the cost of the case.
In order to minimise the complexity and cost of a case, improve robustness and reliability and to maximise the proportion of the overall volume of the case which is available for the accommodation of articles to be transported, it is desirable to avoid the provision of a linkage between wheel carriers and a handle. One approach to attaining this result is proposed in U.S. Pat. No. 4,273,222 where there is proposed a case having a pair of retractable wheels mounted on respective carriers which are pivoted to the main body of the case. An articulated mast, which incorporates a handle, is also pivotally connected with the body. The mast is arranged to co-operate with the wheel carriers to drive the wheels to their projected positions when the mast is raised. When the mast is lowered to the body of the case, the wheel carriers are released for return to their retracted positions by springs. During raising of the mast, the mast and the wheel carriers are pivoted in opposite directions about respective pivots relative to the body of the case.
Proper operation of the mechanism disclosed in U.S. Pat. No. 4,273,222 is dependent upon the maintenance of the required geometry, within close tolerances. With the mast extended, the case is suitable for supporting a stack of additional cases which will impose a heavy load. In order for the required geometry to be maintained when the case is heavily stressed, the case must be of particularly robust construction. This, in combination with the small tolerances permitted, results in an expensive structure. If low weight also is to be attained, for example by the use of composite materials, even greater expense is entailed.
An alternative approach to the provision of a case which has no linkage between the wheel carriers and the handle and which is suitable, when in an extended configuration, for supporting a stack of additional cases, is disclosed in DE No. 2063620. This specification discloses a case having an articulated mast which is connected with a main body of the case for pivoting relative thereto about a pivot axis which lies near to a corner of the case. The wheels are mounted on respective carriers which are fixed to the mast. Pivoting of the mast relative to the body of the case is limited to a range of less than 90.degree.. One consequence of this is that, when the case is in the extended configuration and is used for wheeling a stack of cases on a floor, the clearance between the body of the case and the floor is small. On an uneven floor, for example at a threshold, there is a risk of the case body grounding. This will prevent free wheeling of the case and will result in damage being caused to the case.
The mast of the case proposed in DE No. 2063620 must be open to receive the body of the case between side members of the mast, when the case is in a retracted configuration. The open mast, when in the extended configuration, is an unsatisfactory support for additional cases because these may fall between the side members of the mast.
The wheels of the case proposed in DE No. 2063620, when in the extended configuration, are so positioned that the case cannot stand in a stable manner on a floor whilst supporting a stack of additional cases and with the wheels engaged with the floor. The case can stand in a stable manner on one major face whilst a stack of additional cases is supported on the opposite major face but the wheels will then be raised from the floor. This will inevitably cause damage to the body of the case. Furthermore, the loaded case cannot easily be tipped to bring the wheels into contact with the floor and to raise the body from the floor, for wheeling. This problem is further exacerbated by the fact that the wheels are positioned about as far as possible from the centre of gravity of the case and from the vertical plane containing the centre of gravity of a stack of loaded cases, when the case rests in a stable manner on a floor with the mast upright. Considerable leverage must be applied to tip the loaded case back on to its wheels. Furthermore, remoteness of the wheels from the centre of gravity impairs the stability of the loaded case during wheeling. If the mast is tipped sufficiently far towards the horizontal to bring the centre of gravity over the wheels, then the handle portion of the mast will be at an inconvenient low level.
In one embodiment proposed in DE No. 2063620, the wheels, wheel carriers and mast lie outside the main body of the case, even when in the retracted configuration. This arrangement is likely to result in damage being caused to the case and to other articles with which it comes into contact during handling, particularly mechanical handling on conveyors and carousels. It is proposed in DE No. 2063620 that housings for the wheels and wheel carriers and for an adjacent part of the mast should be incorporated in the main body of the case. These housings constitute a substantial proportion of the overall volume of the case and represent space which is not available for containing articles to be contained in the case, since the housings must be unobstructed, as the mast sweeps through the housings during extension of the mast.
It is an object of the present invention, to provide a case in which one or more of the foregoing disadvantages is avoided.